"Every day they drop several bombs on Azovstal," Petro Andryushchenko, an adviser to Mariupol's mayor, said of the besieged steelworks. "Fighting, shelling, bombing do not stop.''
Cities elsewhere in the Donbas also came under Russian fire overnight, and the attacks interfered with attempts to evacuate civilians.
The region, home to coal mines, metal plants and heavy-equipment factories, is bracing for what could be a decisive campaign as Russian President Vladimir Putin attempts to salvage a victory from the 8-week-old war widely seen as a blunder and a humanitarian disaster.
On Thursday, Putin claimed victory in the battle for the strategic southern port city of Mariupol, even though an estimated 2,000 Ukrainians remained holed up at the sprawling steelworks, which have bombarded for weeks. Putin ordered his troops not to storm the stronghold but to seal it off.
At the same time, Maxar Technologies released new satellite images that it said showed more than 200 graves in a town near Mariupol, and Andryushchenko accused Russia of burying thousands of civilians there.
"The graves have been dug up and corpses are still being dumped there," he said. Initial estimates from the Ukrainians said the apparent mass graves could hold 9,000 bodies, but Andryushenko said there could be more.
Meanwhile, Ukrainian Deputy Prime Minister Iryna Vereshchuk said no humanitarian corridors for civilian evacuations would be open in Ukraine on Friday because it was too dangerous. She urged civilians to "be patient'' and "hang in there.''
"The Russians refuse to open a corridor for civilians, cynically pretending that they do not understand the difference between a corridor for the military to surrender and a humanitarian corridor to evacuate the civilians,'' Vereshchuk said.
Days into the Russian offensive to take the east, the campaign has yet to become a full-out assault, with military analysts saying Moscow's forces are still ramping up. Scattered towns in the east have experienced the thud of incoming shells that drive citizens out in panic.
Slovyansk, a city of about 100,000 in eastern Ukraine, came under fire during the night, according to Mayor Vadym Lyakh, who said no injuries were reported. But he urged residents to leave and said a convoy of buses would be organized. In Rubizhne, Russian fire prevented attempts to bring buses in, Luhansk Gov. Serhiy Haidai said.
Intensive shelling was also heard overnight in Kharkiv, a northeastern city that lies outside of the Donbas but is seen one of the gateways the Russians intend to use to encircle Ukrainian forces in the Donbas from the north, the south and the east.
If successful, the campaign would give Putin a vital piece of the country and a badly needed victory to show the Russian people amid the war's mounting casualties and the economic hardship caused by Western sanctions.
But analysts say Russian forces have yet to have any major breakthroughs in the Donbas. A senior U.S. defense official, speaking on condition of anonymity to discuss the Pentagon's assessment, said the Ukrainians were hindering the Russian effort to push south from Izyum, which lies outside of the Donbas.
"Russian forces continued offensive operations in eastern Ukraine but made only marginal gains,'' according to the Washington-based Institute for the Study of War.
On Friday, Rustam Minnekayev, a senior Russian military official, outlined Russian war aims that appeared to be wider than what the Kremlin has disclosed in recent weeks. He said Russia's forces aim to take full control of not just eastern Ukraine but southern too.
He said such a move would open the way to the nation of Moldova, where Russia backs the breakaway region of Transnistria. Moldovan officials are warily watching Putin's actions in Ukraine.
The battle for Mariupol has been seen as key to the eastern assault. Its capture would free up Russian forces to take part in the larger campaign in the east. But the institute said that Russian troops in the city were probably heavily damaged and that Moscow would struggle to redeploy them quickly.
Mariupol has seen some of the worst suffering of the war, and the satellite images released Thursday hinted at even more.
In the images, long rows of dirt mounds stretch away from an existing cemetery in Manhush, outside Mariupol. Local officials accused Russia of using the graves to try to conceal the slaughter taking place in the city.
There was no immediate reaction from the Kremlin on the satellite pictures. When mass graves and hundreds of dead civilians were discovered in Bucha and other towns around Kyiv after Russian troops retreated three weeks ago, Russian officials denied their soldiers killed any civilians there and falsely accused Ukraine of staging the atrocities.
The U.N. Human Rights office again condemned the Russian invasion.
"Over these eight weeks, international humanitarian law has not merely been ignored but seemingly tossed aside,'' U.N. High Commissioner for Human Rights Michelle Bachelet said.
People fleeing Mariupol have described being trapped in horrible conditions. Yuriy and Polina Lulac said they spent nearly two months living in a basement with at least a dozen other people with no running water and little food.
"What was happening there was so horrible that you can't describe it,'' said Yuriy Lulac, who used a derogatory word for the Russian troops, saying they were "killing people for nothing.''
"Mariupol is gone. In the courtyards there are just graves and crosses,'' he said.
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